package main

import (
	"fmt"
	"math/rand"
	"net/http"
	"net/url"
)

func main() {
	m := map[string]string{}
	s := "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path == "/" && r.Method == "GET" {
			fmt.Fprintln(w, "<h1>shortener</h1>")
			fmt.Fprintln(w, "<form method='POST'>")
			fmt.Fprintln(w, "<input name='url' placeholder='https://example.com'>")
			fmt.Fprintln(w, "<button>ok</button>")
			fmt.Fprintln(w, "</form>")
			return
		}

		if r.URL.Path == "/" && r.Method == "POST" {
			a := r.FormValue("url")

			if a == "" {
				fmt.Fprintln(w, "empty")
				return
			}

			u, err := url.Parse(a)
			if err != nil || u.Scheme == "" || u.Host == "" {
				fmt.Fprintln(w, "bad url")
				return
			}

			b := ""
			for j := 0; j < 6; j++ {
				b = b + string(s[rand.Intn(len(s))])
			}

			for m[b] != "" {
				b = ""
				for j := 0; j < 6; j++ {
					b = b + string(s[rand.Intn(len(s))])
				}
			}

			m[b] = a
			fmt.Fprintln(w, "short url: http://localhost:8080/"+b)
			return
		}

		x := r.URL.Path[1:]
		y := m[x]

		if y == "" {
			fmt.Fprintln(w, "not found")
			return
		}

		http.Redirect(w, r, y, 302)
	})

	fmt.Println("start http://localhost:8080")
	http.ListenAndServe(":8080", nil)
}